1. Field of the Invention.
The present invention relates to a suspension system for use with a surgical microscope and, more particularly, to such a suspension system with vertical movement balancing.
2. Description of Related Art.
In the field of medical technology there exists a need for a mobile surgical microscope suspension system that permits the rapid and nearly effortless movement of the microscope when desired. Illustrative prior suspension systems are disclosed in the following patents: U.S. Pat. No. 2,967,458; U.S. Pat. No. 3,762,797; U.S. Pat. No. 3,776,614; U.S. Pat. No. 3,891,301; U.S. Pat. No. 3,973,748; U.S. Pat No. 4,332,426; U.S. Pat No. 4,523,732; U.S. Pat No. 4,548,373; U.S. Pat. No. 4,741,607; U.S. Pat. No. 4,815,832; U.S. Pat. No. 4,881,709; U.S. Pat. No. 4,953,822; U.S. Pat. No. 5,074,651; and U.S. Pat. No. 5,288,043 (which has common inventorship hereto).
One special need that arises is to be able to move the surgical microscope in the vertical plane, ie. up and down, with a minimum of effort and with a relatively constant resistance or "drag". With all of the prior systems disclosed herein above, very accurate placement of the microscope is hampered by the draw backs inherent therein. Specifically, in prior suspension systems "vertical balancing" has been a problem. Vertical balancing is a desired ability to have the microscope move vertically with little or no inertial movement and with a consistency of smoothness of motion. To achieve vertical balancing, some prior systems use counterweights, such as in the "Contraves" suspension system marketed by Carl Zeiss A.G. of Germany. In other prior systems springs are used which work under compression, such as in the suspension systems used with the surgical microscopes marketed by Moeller.
With the counterweight systems, weights up to about 170-200 kg are used which cause very discernable residual or inertial moment which impairs the surgeon's ability to accurately and quickly position the microscope. With the springs systems, there is variable drag or resistance caused by the spring strength varying with its length of extension. As with the counterbalance systems, this variable spring drag does not permit the smooth and accurate placement of the surgical microscope at the desired height.
There exists a need for a suspension system that is used with surgical instruments that does not have the aforementioned problems.